OF THE GULF OF MANAAE. 
93 
of seeing these forms, and I could not turn aside from what 
I had in hand to place them under a microscope, and as far 
as I had opportunity of seeing, they exactly answered to 
Professor Huxley's description of the larva of the edible 
oyster. I say also " in some measure," above, because I do 
not look upon it as a foregone conclusion that these little 
creatures must be borne by the currents ; they may be able 
to swim agaiust them, as butterflies can in an astonishing 
manner fly against a very strong wind. That butterflies 
can so fly is a fact in natiiral history which is doubtless 
well known, for as my memory serves me it is mentioned 
by Darwin ; and I have myself repeatedly seen butterflies 
crossing the Eed Sea with considerable rapidity in the very 
teeth of a decidedly stiff breeze — I think, from memory with- 
out notes, that I may call it a reef topsail breeze, a breeze 
such that one expected every moment to see a form like a 
butterfly's carried away helplessly before it. And yet the 
butterflies had evidently started on their migration with a 
consciousness of power to battle with the opposing breeze, 
had already accomplished two-thirds or more of their journey, 
and were continuing their course with no uncertain rate of 
progress from the east to the west shores of the Red Sea. 
Taken in this connection, the fact kindly shown me in the 
British Museum that certain patches on the east and west 
shores of the Eed Sea are the habitat of the same butterfly 
is noteworthy. The structure of the butterfly prepares us 
to expect that it would be liable to be tossed about by any 
wind that blows, rather than that it would be able confldently 
to adventure a passage of several miles in the very face of 
it, and across a sea where it could never alight to rest. 
With this example before us it seems to me that we must 
exercise much caution in accepting as conclusive the general 
presumption that the larvae of oysters are borne by the 
currents. I should rather lean to the conclusion that the 
balance of probabiKties is in favor of their being able to 
